Late Mississippian (Chesterian) high-frequency climate change in the Pennington Formation at Pound Gap, KY USA.

Abstract

Climate during the Late Mississippian (Late Chesterian) in the southern Appalachian Basin was characterized by periods of aridity and humidity. The Pennington Formation, exposed at Pound Gap, KY, USA records these changing climatic conditions. The climate signal, however, is partially obscured by longer-term eustatic fluctuations throughout the Late Chesterian. In this clastic-dominated formation, evidence for several orders of cyclicity point to tectonic, glacio-eustatic, and climate controlled-cyclicity. Pennington Formation paleosols provide a record of climate and ecological changes for latest Chesterian time. Forty paleosols were identified, described, and assigned to seven pedotypes ranging from Vertisols to Oxisols. Field and micromorphological evidence suggests a polygenetic character of the Vertisols, resulting from changing soil drainage through time. Using the CIA-K proxy, mean annual precipitation (MAP) estimates range from 519 to 1361 mm/yr. Variations in MAP and quantified soil processes correspond with variation s in soil drainage, resulting from high-frequency paleoclimate change. The temporal distribution of trace elements in paleosols is also related to soil-forming processes and climate. The trace element chemistry (Ti, Ga, Ge, Y, Zr, Nb, Cs, La, Hf, Ta, W, Ce, Th) of the paleosols is controlled by either organic matter content or lessivage (clay formation and accumulation by feldspar weathering). Climate changes are inferred from the trace element chemistry, which is related to changing MAP and intensity of chemical weathering. This study provides greater resolution of changing climate, controls on sedimentation, and pedogenic processes than what is provided in previous studies of the Late Mississippian. The documented variability in fluvial cyclicity, paleosol types, soil drainage, and trace element chemistry might represent the record of high-frequency climate changes likely associated with expansion and contraction of the paleo-Intertropical Convergence Zone (ITCZ).